1. Field of the Invention
The present invention relates to a roller apron which is compatible for casting both a beam-blank strand and a rectangular strand in a curved continuous casting facility.
2. Description of the Related Art
In curved continuous casting facilities of the conventional type compatible for casting both a beam blank strand (nearnet shape) and a rectangular strand, such as billet, bloom or slab, roller apron segments independently equipped with beam-blank rolls and rectangular-strand rolls are prepared and these segments are exchanged with other segments depending on the casting mode for each occasion, i.e. the casting of the beam blank or casting of the rectangular strand. Therefore, a great amount of time and the labor has been required for the operation of the above change over.
Accordingly, to improve the above change-over operation, a curved continuous casting facility which is compatible for casting both the beam-blank strand and the rectangular strand has been proposed in roller apron segments having a fixed frame and a movable frame. On the above fixed frame, web rolls are provided to support the web part of the beam blank or the bottom side of the rectangular strand such as the bloom in the outer portion of the casting radius. On the other hand, the counterpart web rolls are provided on the above movable frame to support the opposite side of the web part of the beam blank or the inner portion of the casting radius of the rectangular strand (refer to the Japanese Utility Model Examined Publication No. 2-11963 and Japanese Patent Examined Publication No. 61-60746 for example).
However, in the above proposed curved continuous casting facilities, because the web rolls disposed in the outside portion of the casting radius are fixed, a curved casting pass line can be maintained with high accuracy. However, as the same web rolls are to be used to support both the web of the beam blank strand (a connecting portion of two parallel sides in the section of, for example, I-section members or H-section members, namely each flange portions and a portion so called web) and the upper and lower surfaces of the rectangular strand (hereinafter, these positions are defined when the bloom is placed horizontally), there is a problem when the beam blank strand having a narrower web width is being cast. Under this circumstance, the web rolls for the combined use axially protrude over the sectional width of the beam blank which result in said rolls engaging with the flange portions of the beam blank, hence, the web rolls cannot support the web. Consequently, there are shortcomings in that not only unsolidified parts tend to remain in the web portion, but also an important tension side in the outer portion of the casting radius cannot be supported positively, and eventually such a problem as bulging will occur.
The following is a detailed description of the aforementioned Japanese Patent Publication No. 61-60746, wherein drum-shape rolls for the combination use of web and bloom are used; however, there is a problem in that when the axial length of the larger diameter portion of the roll is greater than the width of the beam blank, it is difficult to support the web. This is especially true when casting a small beam blank wherein the same problem as described before will occur.